M34 is a cluster of stars that is known as a galactic cluster, or more commonly referred to as an open cluster. A galactic cluster is seen in the night sky as an area in which there appears to be a higher density of stars than other parts of the sky. A commonly known example of a galactic cluster is the Pleiades which is visible with the naked eye in the winter sky. Galactic clusters have no regular shape with hundreds of stars per cluster. The stars in the galactic clusters when analyzed are usually found to be made up of a similar chemical composition to the Sun. Galactic cluster stars seem to be representative of the spiral arms of our galaxy as well as others. M34 in particular was discovered by Giovanni Batista Hodierna before 1654. The age of the cluster has been estimated to be around 180 million years by G. Meynet's Geneva Team. The cluster lies about 1,400 light years away and can be seen in the night sky as it is found just north of the line between Algol (Beta Persei) and Gamma Andromedae.

This image displays the northeastern corner of M34. The cluster is scattered over about 35 arc minutes, which is more than the diameter of the full moon. This angular diameter corresponds to about 14 light years. In the lower right hand corner of the picture the edge of the cluster is shown as the group of relatively bright white stars and several red giants that are close to one another. At both the top center and upper right portions of the image there are two very bright orange stars. These stars, however, are not part of the open cluster. In the actual cluster we see that there are stars that are burning white/blue and others that are more of a reddish orange. The different colors of the stars are due to the different temperatures at which they burn- the blue being hotter and the red being cooler. The fact that there are red giants in the star cluster tells us that the cluster is middle aged because the red giants were previously burning blue before they began to cool down into a red giant.When the composition of the stars in this open cluster are analyzed, over 90% of the atoms are hydrogen and most of the rest are helium. As stated previously this is a similar composition to that of the Sun in our solar system.

References:

Frommert, Hartmut and Kronberg, Christine. "Messier 34." Students for the Exploration and Development of Space.